The present invention is related to retroreflective devices, particularly those of the type employed on roadways.
Retroreflective devices have been used for some time in marking roadways and in providing similar marking functions. Typically, the retroreflectors are used outdoors in a wide variety of environmental conditions, and in some applications they are used in large numbers. In addition, those used on roadways are often subjected to repeated impact from passing traffic. Accordingly, low cost and durability are among the criteria for determining whether or not a given retroreflective device is to be used. It is also desirable that the device be simple to manufacture, easy to use, and readily replaceable. All of these features should be provided in a structure that is highly visible to someone in an oncoming vehicle regardless of weather conditions. Since roadway reflectors must stand up to the impact of passing traffic, it is also desirable for the retroreflector to present a low profile. Of course, the requirement of high visibility and the presentation of a low profile are conflicting to an extent, so it is important to effect the best tradeoff possible between these two requirements.
Although the number of types of retroreflective devices precludes an exhaustive listing here, an exemplary type is illustrated generally in U.S. Pat. No. 3,519,327 to Nakajima. In this type of retroreflective device, a reflecting surface is provided by an interior block that is covered by refractive material. In the device specifically described in the Nakajima reference, the retroreflective structure is provided by a vertical surface on the block. The surface is made up of a series of vertical planes that intersect at right angles. This vertical surface cooperates with a horizontal reflecting surface to provide the desired retroreflection. It is apparent that such a device is somewhat elaborate. Although it could conceivably be used in quantity, it is likely that the attendant cost would be high.
An attempt to meet the need for a low-profile retroreflective device is illustrated in U.S. Pat. No. 4,145,112 to Crone, in which the retroreflective surface is disposed horizontally in a strip to be applied to the roadway. The substantially horizontally traveling light rays are diverted to the retroreflective surface by the provision of transparent ridges above the retroreflective surface whose faces are at such an angle as to reflect light down to the retroreflective surface. Unfortunately, this type of an arrangement requires a rather large amount of retroreflective surface for a given amount of image. Furthermore, as the teachings of the present invention will show, simpler devices are possible.
U.S. Pat. Nos. 3,920,346 to Wyckoff and 4,129,397 to Eigenmann avoid the problems presented by horizontal retroreflective surfaces. Both arrangements disclose vertically oriented retroreflective surfaces, so the amount of retroreflective surface required for given image is not as great as the amount required by the Crone device. The arrangements illustrated in FIGS. 1-3 of the Eigenmann reference describe a relatively simple device in which a retroreflective insert is received in a groove in a refractive body. Although simple, this arrangement leaves the retroreflective surface generally unprotected, and the groove is thought to make the refractive body somewhat weak structurally. Wyckoff, on the other hand, does appear to provide some kind of covering for the vertical retroflective piece; moreover, the vertical piece appears to have been provided in the form of a relatively thin strip, which has obvious advantages in simplicity and ease of construction. Again, however, the cavity provided for the sheet material would appear to significantly weaken the surrounding transparent structure because the sealing coating above the sheet material is quite thin. Also, a coating that is too thin is likely to be worn away enough so that foreign matter can find its way onto the retroreflecting surfaces and thus reduce visibility.
It is for the purpose of reducing some of the drawbacks of prior-art retroreflectors that the retroreflective device of the present invention has been developed. It is an object of the present invention to permit a relatively low profile in a device that is highly visible. It is a further object of the present invention to afford these advantages in a structure that is easy to manufacture, simple to install, and rugged.